We developed a new spectroscopic reflectance-based method of detecting alterations in biological tissues which are related to the early stages of cancer formation. We used setup based on diffuse reflectance spectrometer to collect data in the clinical settings The white light excitation for measured reflectance data was provided by a compact 4J/pulse xenon arc lamp (EG&G, model FX-249). The lamp provides a pulse width of 10 ms. Excitation beam was coupled into a 200 fm core diameter optical fiber (0.22 NA). By using pulsed excitation of white light source and gated detection of reflectance signal, background signal from illumination source was minimized. Data acquisition is controlled by a 486-notebook microcomputer. The study employs collection of reflected spectra in colon during hospital endoscopy procedures and processing them using physical model. The model takes into account propagation of light in presence of oxy- and de-oxy- hemoglobin and scattering on coll agen fibers. This study has shown that: (a) it is possible to measure the optical properties of human colon tissue in vivo by employing a physical model describing tissue diffuse reflectance, and (b) the optical properties measured can be correlated with the biochemical and morphological composition of tissue, which can be useful for the detection of disease.